A severe drought has pushed river levels in Brazil's Amazon region to record lows, leaving isolated communities dependent on emergency aid and thousands of boats stranded on parched riverbeds.

The drought fits a pattern of more extreme weather in the world's largest rain forest in recent years and is, scientists say, an expected result of global warming. Last year, the region was hit by widespread flooding and in 2005 it endured a devastating drought.

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The level of the dark Rio Negro, a tributary to the Amazonas river and itself the world's largest black-water river, fell to 13.63 meters (45 feet) on Sunday, its lowest since records began in 1902, according to the Brazilian Geological Service. Only last year it hit a record high of 29.77 meters (98 feet).

The shallow water has exposed sandbanks and rocks and has made part of the river unnavigable. Life in the vast Amazon river network depends to a large extent on boat transport.

"People are lacking food because fish are dying in the warm waters. Nearly all boats are grounded -- only the smallest ones can navigate the waters," said Rosival Dias, a coordinator with the Amazonas Sustainable Foundation environmental group who has visited affected areas.

"I've worked in the region about 30 years and never seen anything like the last few years. This has everything to do with climate change."

Amazonas state says the emergency has affected 62,000 people in 38 municipal areas, and that 600 tonnes of food aid has been distributed by plane and boat. The Brazilian government announced last week it was releasing 23 million reais ($13.5 million) in emergency aid.

Soy producers that rely on the Madeira river in Amazonas state to ship barges of the food product have been forced to divert loads at great expense to ports in the southeast of the country some 2,000 km (1,250 miles) away.